Exciplex host SiCzCz:SiTrZCz2 has a triplet energy level that is lower than those of single host materials but still high enough to allow the exciplex to be used as a co-host in blue phosphorescent organic light-emitting diodes (PhOLEDs). Also device using mCBP:SiTrZCz2 (mSi-2CzTrz) as exciplex host demonstrated an external quantum efficiency of 22.8% and a operational lifetime with up to 80% of the initial luminance of over 2000 h at 100 cd m−2 in blue PhOLEDs [1].